translate([0,0,99])
difference(){
intersection(){
difference(){
sphere(106.0,$fn=150);

translate([-200,-200,0])
cube([400, 400, 400],center=false);

}
translate([-200,-200,-99.0])
cube([400, 400, 400],center=false);

}
intersection(){
sphere(100.0,$fn=150);

translate([-200,-200,-93.0])
cube([400, 400, 400],center=false);

}
}
